1. Field of Invention
The present invention relates to a projector for projecting a modulated light in enlarged form on a projection screen through a projecting means as a result of modulating light from a light source by a light modulating element in accordance with image information.
2. Description of Related Art
A projector primarily comprises a light source unit; an optical unit for optically treating the light from the light source unit so as to synthesize color images in accordance with image information; and a projection lens for projecting in enlarged form the synthesized light onto a screen.
FIG. 14(A) is a schematic structural view of the optical unit and the projection lens. As shown in this figure, the optical system of the optical unit 3 comprises a light source 20 included in a light source unit; a color separation optical system 40 for separating a light W, emitted from the light source 20, into the three primary color light beams, namely, the red light beams (R), the green light beams (G), and the blue light beams (B); three liquid crystal panels (light modulating elements) 5R, 5G, and 5B, for modulating each of the different color light beams in accordance with image information; a cross dichroic prism 60 for combining each of the modulated color light beams; and a projection lens 4 for projecting in enlarged form the synthesized light onto a screen 120. The light W, emitted from the light source 20, is separated into the respective color light beams, R, G, and B, by the color separation optical system 40 comprising various dichroic mirrors. Of the color light beams, the red light beams R and the green light beams G are directed towards corresponding liquid crystal panels 5R and 5G from their corresponding light-outgoing portions in the color separation optical system 40. The blue light beams B are guided towards the liquid crystal panel 5B via a light-guiding optical system 50.
In the optical unit 3 illustrated in enlarged form in FIGS. 14(B) and 14(C), polarizers 100R, 100G, and 100B are disposed adjacent to the light-incoming surface of corresponding liquid crystal panels 5R, 5G, and 5B. The polarizers 100R, 100G, and 100B are provided to align the polarization planes of the different color light beams incident upon the corresponding liquid crystal panels 5R, 5G, and 5B. Polarizers 110R, 110G, and 110B are disposed at the light-outgoing side of the corresponding liquid crystal panels 5R, 5G, and 5B. The polarizers 110R, 110G, and 110B are provided to align the polarization planes of the different modulated color light beams that are going to strike the cross dichroic prism 60. The polarizers allow an image with high contrast to be projected onto the screen 120. Of the polarizers sandwiching their corresponding liquid crystal panels 5R, 5G, and 5B, the polarizers 110R, 110G, and 110B positioned at the light-outgoing surface side of the liquid crystal panels are adhered to the light-outgoing surface of their corresponding liquid crystal panels.
A generally used polarizer consists of a polarizer and a protective layer laminated thereto, with the polarizer formed of a dichroic material such as an iodine-containing material or organic dye. For the liquid crystal panels, an active matrix type liquid crystal device is generally used, in which type of liquid crystal device the pixels disposed in a matrix arrangement are controlled by a switching element.
Here, an effective way of increasing contrast of the image projected in enlarged form onto the screen 120 is to adhere a polarizer with good polarization selection characteristics to the light-outgoing surface of each of the liquid crystal panels 5R, 5G, and 5B. However, polarizers with excellent selection characteristics correspondingly absorb a larger amount of light, so that a large amount of heat is generated thereat. The above-described projector is constructed so that the polarizers are cooled by air currents formed in the projector, as shown in FIG. 14(C). However, since the polarizers are directly adhered to the light-outgoing surface of their respective liquid crystal panels, the liquid crystal panels transmit heat easily, so that the temperature of the liquid crystal panels tends to rise. This temperature rise deteriorates optical characteristics of the liquid crystal panels, reducing contrast of the projected image.
A possible solution to this problem is to dispose the polarizers so that they are separated from the light-outgoing surface of their respective liquid crystal panels. However, when the polarizers are merely separated from their respective light-outgoing surfaces, dust or the like sticks onto the light-outgoing surface of the liquid crystal panels by the air currents flowing in the device, causing a reduction in the quality of the projected image.
In view of the above-described problems, it is an object of the present invention to provide a projector which can project a high quality image, without deteriorating the optical characteristics of the light modulating elements and without allowing sticking of dust or the like onto the light-outgoing surface of the light modulating elements.
To overcome the above-described problems, according to the present invention, there is provided a projector comprising a light-modulating element for modulating light emitted from a light source in accordance with image information, and projecting means for projecting the light modulated by the light modulating element in enlarged form onto a projection surface;
wherein a polarizer is disposed adjacent to the light-outgoing surface side of the light-modulating element, and a dust protection member is provided so as to cut off from the outside the area between the polarizer and the light-outgoing surface of the light-modulating element.
In the projector of the present invention, a dust protection member is provided so as to cut off from the outside the area between the polarizer and the light-outgoing surface of the light-modulating element, thus forming an air layer between the polarizer and the light-outgoing surface. Therefore, the amount of heat generated at the polarizer and transmitted to the light-modulating element is reduced by the air layer. Consequently, even when a polarizer with excellent selection characteristics is used, the amount by which temperature of the light-modulating element rises by heat generated at the polarizer can be reduced, thereby obviating the problem of deterioration in the optical characteristics of the light-modulating element.
The area between the polarizer and the light-modulating element is cut off from the outside, so that even when dust or the like is scattered by air currents produced in the display interior, the dust does not enter into the area therebetween. Therefore, it is possible to eliminate the problem of dust or the like sticking onto the light-outgoing surface of the light-modulating element.
Accordingly, the projector of the present invention can project a high quality image with excellent contrast onto a projection surface, without deteriorating the optical characteristics of the light-modulating element and without allowing dirt to stick onto the light-outgoing surface of the light-modulating element.
When a polarizer is also disposed at the light-incoming surface of the light-modulating element, it is preferable to cut off from the outside the area between the polarizer and the light-incoming surface of the light-modulating element with the dust protection member. The dust protection member can prevent dirt from sticking onto the light-incoming surface of the light-modulating element, and is effective in allowing projection of a high quality image.
When a transparent plate is disposed between the light-incoming surface of the light-modulating element and the polarizer disposed adjacent to the light-incoming surface, it is desirable to cut off from the outside the area between the transparent plate and the light-incoming surface of the light-modulating element by the dust protection member. When the dust protection member is provided, the air layer between the transparent plate and the light-modulating element, and the transparent plate are interposed between the polarizer and the light-modulating element, so that the amount of heat generated at the polarizer (disposed adjacent to the light-incoming surface of the light-modulating element) and transmitted to the light-modulating element can be reduced. In addition, it is possible to prevent dust from sticking onto the light-incoming surface of the light-modulating element.
When dust or the like tends to stick onto the light-incoming surface of the light-modulating element by, for example, air currents generated in the device, a dust protection member can be used to cut off from the outside the area between the polarizer and the light-incoming surface of the light-modulating element.
Not only can a commonly used polarizer be of the type which transmits one type of polarized light and absorbs the other type of polarized light. It can also be a reflective type polarizer which reflects the other type of polarized light. The reflective type polarizer absorbs only a small amount of light, and thus generates only a small amount of heat. Therefore, the reflective type polarizer can reduce the amount by which the temperature of the light-modulating element rises. When a reflective type polarizer is disposed adjacent to the light-incoming surface of the light-modulating element, it is possible to prevent the light-modulating element from being irradiated with light reflected from the polarizer, thereby obviating the problem of a malfunction of the light-modulating element caused by light reflected by the polarizer.
The present invention not only applies to a projector with one light-modulating element, but also to a projector with a plurality of light-modulating elements. More specifically, the present invention may be applied to a projector comprising color separation means for separating the light from the light source into a plurality of color light beams; a plurality of the light-modulating elements for modulating the respective color light beams in accordance with image information; color synthesizing means for synthesizing the respective color light beams modulated by the light-modulating elements; and projecting means for projecting in enlarged form the flight synthesized by the color synthesizing means onto a projection surface.
In this projector, it is desirable that each light-modulating element and each polarizer be supported by a dust protection member, and that each dust protection member be removably affixed to the light-incoming surface of the light synthesizing means. In this case, it is not necessary to directly touch the light-modulating element in order to mount it at the side of the color synthesizing means, so that it is possible to eliminate the problem of breakage or defects which occur in the light-modulating element when it interferes with other component parts. It is also possible to facilitate replacement the light-modulating element.